Magnetic laminations for high frequency inductors



March 22, 1960 D. s. CONNELLY MAGNETIC LAMINATIONS FOR HIGH FREQUENCYINDUCTORS Filed Oct. 3. 1957 34 FIG. 6

INVENTOR. DANIEL s. conuzu; BY 2 2 ATTORNEY FIG? United States PatentMAGNETIC LAMINATIONS FOR HIGH FREQUENCY INDUCTORS Daniel S. Connelly,Cleveland, Ohio, assignor to The Ohio Crankshaft Company, Cleveland,Ohio, a corporation of Ohio Application October 3,1957, Serial No.688,026 2 Claims. C1. 219-1o.79

This invention pertains to the art of induction heating, and moreparticularly to a construction and arrangement of magnetic laminationsfor use with alternating current induction heating coils.

, In the art of induction heating, it is often necessary to I positionthe magnetic laminations about a helical coil with the plane of thelaminations disposed generally in the axial, radial plane. With such anarrangement, in order for the laminations to be packed in tightly in acircumferential direction so as to obtain a high stacking factor, i.e.,the maximum amount of magnetic material in a circumferential direction,it has heretofore been necessary to resort to expensive expedients inorder to compensate for the increasing circumference in a radiallyoutward direction. Thus, it is known to grind the laminations to a wedgeor pie shape. This is an expensive operation, and is difiicult toperform on relatively thin sheets of magnetic material. Furthermore, thegrinding operation oftentimes affects the orientation of the grains ofmetal to impair the magnetic characteristics of the material.

It is also known to provide some of the laminations having a full radialwidth and other laminations of a lesser radial width which are stuffedinto and between the full width radial laminations. This is an expensiveoperation and requires the handling of a large number of different sizesof parts, and makes difficult the retaining of the narrow laminations inposition.

The present invention contemplates a magnetic lamination constructionwhich overcomes all of the above-referred to difficulties, and enables ahigh stacking factor to be obtained using lamination material of uniformthickness and of uniform radial width.

In accordance with the present invention, a plurality of magneticlaminations are provided adapted to be disposed to form a generalcylinder with the planes of the laminations in the axial radial plane ofthe cylinder, the laminations having a uniform radial dimension andbeing formed from a sheet of uniform thickness and so constructed andarranged that when assembled the laminations will abut at least alongthe inner periphery of the cylinder, and at least at a point close tothe outer periphery thereof.

In one embodiment of the invention, each lamination is formed from athin sheet of magnetic material having the outer periphery thereoffolded back upon itself in such a manner that the increased thickness atthe edges makes up for the increased circumference of the stack adjacentthe outer edges.

In other embodiments of the inventio'n, the alternate portions of theinner edges of adjacent laminations are cut away so that the portionsremaining may overlap in a circumferential direction so as to providecircumferential contact of adjacent laminations at the inner peripheryand adjacent to the outer periphery thereof.

The principal object of the invention is the provision ofa new andimproved lamination arrangement having a high stacking factor andemploying lamination material of a uniform radial width and employinglamination stock of a uniform circumferential thickness.

Another object of the invention is the provision of a new and improvedmagnetic lamination arrangement of the type described wherein all thelaminations may have the same radial width.

Another object of the invention is the provision of a new and improvedarrangement of magnetic laminations wherein a high stacking factor canbe obtained without the use of laminations ground to a taperingthickness.

The invention may take physical form in certain parts and arrangementsof parts preferred embodiments of which will be described in detail inthe specification, and illustrated in the accompanying drawing which isa part hereof and wherein:

Figure 1 is a fragmentary side cross-sectional view of a high frequencyinductor embodying the present invention, the section being takenapproximately in the line 1-1 of Figure 2;

Figure 2 is a cross-sectional view of Figure 1 taken approximately inthe line 22 thereof;

Figure 3 is a view somewhat similar to Figure 1, but showing analternative embodiment of the invention;

Figure 4 is a cross-sectional view of Figure 3 taken approximately onthe line 4-4 thereof;

Figures 5 and 6 are plan views of the individual laminations employed inthe embodiments of Figure 3; and

Figure 7 is a view similar to' Figure 3 but showing a still furtheralternative embodiment of the invention.

Referring now to the drawing wherein the showings are for the purposesof illustrating preferred embodiments of the invention only and not forthe purposes of limiting the invention, the figures show a highfrequency inductor construction particularly intended for internalheating and comprised of a hollow shaft or tube 10 having mounted on thelower end thereof the inductor per se which with the exception of thelamination arrangement is relatively conventional in the art. Thus theinductor consists of a multi-turn helical coil 12 of hollow coppertubing embedded in suitable electrical insulating material 13. The outersurface of the coil is adapted to face a metallic workpiece and inducehigh frequency electrical currents to flow therein. Surrounding theupper, lower, and inner sides of the coil 12 are magnetic laminationsconstructed in accordance with the invention, and in particular,consisting of a plurality of individual laminations stacked into acircular stack with the plane extending parallel to the axis of the coiland generally parallel to the radius of the coil. Each of thelaminations have on their inner corner axially extending lugs 16 whichare overlapped by a shoulder 17 on a ring 18 mounted on the tube 10.Thus, the ring 18 fits against a shoulder 19 on the tube 10. In a likemanner, a lower ring 22 is provided which is identical to the ring 18which engages a lower projection 23 on the laminations. A nut 25threaded on the lower tube 10 clamps the rings 18, 22 over the shoulders16, 23 respectively, to hold the laminations in position.

There is thus a circular stack of laminations each disposed in the axialradial plane of the inductor. It will be appreciated that thecircumference of the stack at its inner periphery is substantially lessthan that at the outer periphery. Thus, if the laminations 15 all had auniform circumferential thickness, there would be substantial clearancesbetween the outer edges of the laminations and thus a poor stackingfactor. The present invention deals directly with this problem.

Thus, in accordance with the preferred embodiment of the invention, eachlamination has a portion 26 integral with the lamination which doublesback on itself in close space relationship therewith. The effect of theportion 26 is to increase the circumferential width or 'the' radialwidth of the laminations.

thickness of each lamination adjacent its outer edge. The stackingfactor at the outer edge is thus substantially improved. The individuallength of the portions 26 may be as desired to give the improvedstacking factor. Usually the individual laminations will be made so thatthe portions will have a variety of different lengths so as to provideand improve the stacking factor over generally the entire radial widthof the stack. The length of the portions 26 will vary depending upon thediameter of the inner and outer edges of the laminations stacked, butthey should be made so that tight packing will occur on at least onecircumferential point radially outwardly from the inner edge of thelaminations. Thus, it will be apparent that the laminations will alwayshave a tight stacking factor at the point 28. Furthermore, because ofthe portions 26, it will be possible to have a tight stacking factor atany desired point along By varying the length of the portions 26, it ispossible to have a plurality of lines having a tight stacking factorcircumferentially around the stack.

Using the present invention, it will be appreciated that all of thelaminations have a uniform radial width. This makes their handling andassembly much easier than if a plurality of different radial widths oflaminations were employed. Also using the present invention, the needfor grinding a taper onto thin lamination material is avoided.

Figure 3 shows an alternative embodiment of the invention. Thelaminations in this embodiment have generally the same radial width asthat of the preferred embodiment. However, the inner edge of onelamination is cut away, as at 30 in Figure 5, leaving radially extendingportions 31,32, in spaced'relationship. These portions 31, 32 have thelugs 16, 23 formed thereon. The adjacent lamination has a portion atboth corners 'cut away as at 33, 34 to correspond with the portions 31,32 and leaving a portion 35 to correspond with the cut-out portion 30 ofthe other lamination. Thus, the portion 35 nests into the cut-outportion 30. The effect is that the laminations can then have a tightstacking factor on the inner periphery and along the line 38corresponding to the edge 39 of the cut-out portion 30. If desired, theradial depth of the cut-out portion 30 may be varied from each set oflamination to the other so as to improve the stacking factor over amultiplicity of points. Thus, generally alternate portions of at leastone-half of the inner edges are cut away.

Figure 7 shows a still further alternative embodiment of the inventionwherein one corner 41 on the inner edge and of an axial lengthapproximately equal to onehalf the axial length of the lamination is cutaway.

Then by orienting the laminations one relative to the other, theremaining portion 40 of one can be made to nest into the cut awayportion of the other. A result similar to the stacking of Figures 5 and6 results.

Using the present invention, it has been found possible to obtain highstacking factors at a minimum expense. Such high stacking factors aredesirable and necessary if high flux concentrations are to be employedwith the induction heating coil 12.

Obviously, the invention is not limited to internal type inductors,butmay be employed with external type inductors.

The invention has been described with reference to preferredembodiments. It will'be appreciated that'modifications and alterationswill occur to others upon the reading and understanding of thisspecification, and it is my intention to include all such modificationsand alterations insofar as they come within the scope of the presentclaims.

Having thus described my invention, I claim:

1. A high frequency induction heating coil comprising a helical coil anda cylindrical lamination stack composed of a plurality of separatemagnetic laminations associated with said coil, each of said laminationscomprising a radially outwardly extending leg of uniform thickness whichlies substantially in an axial radial plane of the coil, said outwardlyextending legs of the several l-aminations having equal radial lengthsand abutting against each other at their inner radial ends, each of saidlaminations at its outer radial end being doubled back upon itself andpresenting a radially inwardly extending return leg of the samethickness, said return leg of each lamination throughout substantiallyits entire extent radially inward lying flat against the outwardlyextending leg of said lamination and engaging the outwardly extendingleg of the next lamination radially inward from the outer radial endthereof.

2. The heating coil of claim 1 wherein the return legs of neighboringlaminations have different radial lengths.

References Cited in the file of this patent UNITED STATES PATENTS1,644,729 Johannesen Oct. 11, 1927 1,801,214 Von Henke Apr. 14, 19312,498,702 Nahman Feb. 28, 1950 2,516,140 Nahman July .25, 1950 2,596,770Groven May 13, 1952 2696,593 Dole Dec. 7, 1954 2,743,345 Seulen et alApr. 24, 1956 2,761,048 Tudbury Aug. 28, 1956

